The aim of the proposed research is to determine whether an individual has acquired an adult reading vocabulary and to develop effectiveness measures of growth towards adult competence in vocabulary. Adult standards are defined by previously identified adult corpora. In Phase I, word frequencies will be calculated and checked against published counts for these corpora. Other corpora, defined by materials written for students from early grades on, will be analyzed. Counts will be conditioned on prose difficulty, because variability in book difficulty defined by publishers' grade level designations is exceedingly large. Phase I word frequency counts will be twice the size of the largest published school corpora. Vocabulary measures are developed in Phase II. Stratified samples from the frequency bands of the adult corpus will be drawn to test for lexical meanings. Latent trait models and TASA's calibration designs will be used to obtain sample-free estimates of vocabulary item difficulty. Phase II research should show that several factors account for difficulty of vocabulary test items, including the frequency of the word in the adult corpus, the relative frequency of the word in corpora that form the development scale, and the relative frequency of the word's lexical meaning.